except IndexError:
# Don't try keys that are too long
break
edit_dist_1 = float(util.edit_dist(first_bytes, second_bytes)) / key_len
edit_dist_2 = float(util.edit_dist(second_bytes, third_bytes)) / key_len
edit_dist_3 = float(util.edit_dist(third_bytes, fourth_bytes)) / key_len
avg = (edit_dist_1 + edit_dist_2 + edit_dist_3) / 3
lens_and_distances.append((key_len, avg))
best_keysizes = sorted(lens_and_distances, key=lambda tup: tup[1])[0:
N_KEYSIZES]
print(best_keysizes)
for (keysize, score) in best_keysizes:
# Break the ciphertext into blocks of size KEYSIZE, and transpose the
# blocks so that the first char of the first block goes with first char
# of second block, second chars go together, etc.
transposed_blocks = break_and_transpose(ctext, keysize)
full_key = ''
# Next, solve each block as though it was single-character XOR to find
# that part of the key. Put the best guesses for the single-character
# keys together and use these to guess the actual key.
for block in transposed_blocks:
(_, _, key) = util.solve_single_char_xor(block)
full_key += key
# Correct plaintext isn't top result for the example (6.txt), but it's
# in the output. :D
print('Key: ' + full_key)
print(util.xor_repeating(ctext, full_key))
"""Repeating key XOR. Function is implemented in util, an example of usage is
here."""
from util import xor_repeating
PLAINTEXT = ("Burning 'em, if you ain't quick and nimble\n"
"I go crazy when I hear a cymbal")
KEY = 'ICE'
if __name__ == '__main__':
print(xor_repeating(PLAINTEXT, KEY).encode('hex'))
